Transcript regional O 3 - Center for Air Pollution Impact and Trend Analysis

Telling the OTAG Ozone Story with Data
OTAG Air Quality Analysis Workgroup
Dave Guinnup and Bob Collom, Workgroup co-chair
Volume I: EXECUTIVE SUMMARY
June 2, 1997
Workgroup Objective
The Workgroup is to provide assessments of air quality
and meteorological data relevant to the mission of OTAG.
OTAG mission:
To understand the role of transported ozone and precursors
in the current ozone nonattainment problem
Description of the Air Quality Analysis WG
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AQA WG members were affiliated with EPA, state agencies,
industry (power,transportation), consultants, academia
Members were analysts or research managers generally
representing their organizations
Interaction occurred through meetings, conference calls (monthly),
and e-mail
Sharing of reports, data and comments was conducted through the
AQA-WG interactive web site. (http:\\capita.wustl.edu\OTAG\)
Types of Analyses
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Spatial pattern percentile analyses
Trajectory residence time analyses
Spatial, temporal correlation analyses
Statistical cluster analyses
Model/data comparisons
Tracer analyses
Temporal pattern and trends analyses
Meta analysis: analysis of analysis
Results integration
Problem Statement
From the OTAG Background Document:
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Some nonattainment areas (e.g. NE corridor, Lake Michigan)
experience considerable influx of ozone across their boundaries
They cannot demonstrate nonattainment by local measures only
Significant ozone reductions at their boundaries will also be
necessary
More counties are in nonattainment of the 80 ppb than the
120 ppb standard. Transport is also more important at the 80
ppb exceedance level.
Area source NOx emissions are highest near cities.
Point sources dominate the center of OTAG.
Area Source Density of NOx
Point Source Density of NOx
The OTAG domain corners are at tropospheric O3 levels.
The highest avg. O3 is over the megalopolis and Ohio Valley.
There is an increasing trend from west to east.
Highest (90 %-ile) O3 occurs near urban areas.
Lowest (10 %-ile) O3 is high in the center of the domain.
90th percentile of daily max. O3
10th percentile of daily max. O3
Northeast O3 exceedances have been declining.
OTAG domain exceedances show less decline.
Ten year station-day
exceedances for the Northeast.
Ten year station-day exceedances
for the OTAG domain.
At slow wind speeds, O3 accumulates near source areas.
At high wind speeds, O3 is dispersed from sources.
The dispersion leads to long range transport and regional O3.
Average ozone during low
(< 3 m/s) wind speeds.
Average ozone during high
(>6 m/s) wind speeds.
In the South, higher winds reduce O3, in the North it does not.
In the Northeast, regional O3 is transported by synoptic and
channeled flows while local O3 by near surface flows.
Relative change of ozone
concentration with wind speed.
Flow regimes over the
Northeast.
On high O3 days, the transport winds are slow with clockwise
circulation around the south-center of the domain.
On low O3 days, the swift transport winds are from outside the
domain.
Transport winds during high
(90%-ile) local ozone days.
Transport winds during low
(10%-ile) local ozone days.
During regional episodes, air masses meander over the high
emission regions and accumulate O3. The implied range of O3
transport is 150 - 500 miles.
The ‘88,‘91,‘95 modeling episodes lasted 6-9 days.
Ozone pattern and air mass histories
during the 1995 episode.
Daily maximum ozone averaged
over all monitors in the domain.
The 4 episode avg. model concentration shows high O3
over the central section of the domain.
The model O3 pattern roughly corresponds to the data.
Measured average daily maximum
O3 during the four episodes.
Model-average daily maximum O3
during the four episodes.
The model under-predicts O3 in the North and over-predicts in
the South by 10-20 ppb.
The modeling periods over-represent O3 in the North and
under-represent O3 in the South.
Difference between UAM-V model
prediction and measured O3.
Difference between the OTAG domain
episodes and the 90th percentile O3.
Transport winds during the ‘91,‘93,‘95 episodes are
representative of regional episodes.
OTAG episode transport winds differ from winds at
high local O3 levels.
Comparison of transport winds during
the ‘91, ‘93, ‘95 episodes with winds
during regional episodes in general.
Comparison of transport winds
during the ‘91, ‘93, ‘95 episodes with
winds during locally high O3.
OTAG is a well defined control region. Low O3 air comes
from outside, high O3 air from inside OTAG.
Back trajectory frequencies
for low ozone days.
Back trajectory frequencies for
high ozone days.
The transport winds on high O3 days are slow in the
center of the domain.
At many sites, the avg. O3 is higher when the wind blows
from the center of the domain.
Superposition of O3 contours and
transport winds during high (90th
percentile) O3 conditions.
Ozone roses for selected 100 mile size
sub-regions.
Emission changes do change O3 levels. 120 ppb exceedances
are 3 times higher on Fridays than on Sundays.
Map of exceedances on Fridays.
Map of exceedances on Sundays.
Conclusions of the OTAG AQA Workgroup
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Slow winds cause local ozone episodes near urban areas. VOC reductions
are effective for 'peak shaving' near such urban areas. High winds disperse
local ozone but cause regional ozone through long-range transport. The
implied range of ozone transport from various studies is between 150 and
500 miles.
Stagnation over multi-state areas followed by transport results in regional
ozone episodes. The central area of the OTAG domain is frequently
associated with such regional episodes. NOx controls within that area would
benefit many nonattainment areas downwind
The OTAG UAM-V model simulations are useful for emission scenario
evaluations since they reproduce the gross ozone pattern and they are
representative of regional ozone episodes. However, the model appears to
understate the range of ozone transport and it poorly represents the
conditions when most exceedances occur.